1. Field of the Invention
This invention relates to telecommunications systems, especially PBX/Server systems, also referred to as Multi-Line Telephone Systems (MLTS). Specifically, the invention relates to completing an emergency, e.g. 911, call from a station/device behind a PBX or MLTS to a public safety answering point (PSAP) such that the PSAP can call back the emergency caller even though the station/device does not have a direct inward dial (DID) number.
2. Brief Description of Related Art
When a caller calls an emergency number, e.g. 911, the call is routed to a Public Safety Answering Point (PSAP). In some jurisdictions, regulatory agencies require that the caller""s telephone number/callback number and/or precise physical location referred to as Location Identification Number (LIN), be automatically provided to the PSAP. This information is used to locate the caller and to call back to the caller should there be an unintended disconnect. This caller identification (i.e., telephone number and LIN) may be delivered to the PSAP either in-band (e.g., using DTMF/MF signaling) or out-of-band (e.g., using ISDN signaling) depending on the type of trunk circuit employed. For residential callers, the LIN may simply be the street address or the street address and apartment number. For commercial callers, the LIN needs to be more complex, for example, street address, floor number, room number, desk number. In some cases, the LIN is geodetic, i.e. includes earth coordinates or GPS data.
Modern PBX/MLTS systems provide many new features to accommodate the way modern businesses operate. For example, employees may be assigned personal identification numbers (PINs) that are used by the PBX/MLTS to identify the employee and assign a telephone number to him/her. For example, if an employee is assigned to a different location in the building, an automatic relocation feature can be activated using the PIN to reassign the employee""s telephone number to the new location. Another feature of PBX/MLTS systems is that some telephones connected to the PBX/MLTS system may not be provided with the ability to receive direct dialed calls. For example, in a hotel, telephones in rooms are typically not capable of receiving a direct inward call from outside the hotel. All outside calls must pass through the switchboard operator. Still another feature of modern PBX/MLTS systems is that it is possible to make many or even all telephone lines available for use by multiline devices connected to the system. Thus, a caller from behind the PBX/MLTS system may be identified by many different telephone numbers.
In many situations, the only callback number provided from the PBX/MLTS system is the main billing number. In situations where the caller has no direct inward call receive capability, the PSAP cannot quickly call back the caller in the event of a disconnect. In the situation of a call from a multiline device, the telephone number from which the emergency call is made may not be the primary number for the caller and a return call to that number may cause a different device to ring rather than the caller""s device. Moreover, the number used by the emergency caller may be associated with a LIN which is not the caller""s LIN.
A method may be used for reporting the LIN of an emergency caller behind a PBX/MLTS system to a PSAP. The method includes assigning a port equipment number (PEN) to each port associated with the PBX/MLTS system, maintaining a database of LIN and callback numbers associated with PENs, identifying an emergency number when it is dialed, invoking an emergency service routing upon detection of a dialed emergency number, associating the PEN with the dialer of the emergency number, retrieving the LIN and callback number from the database, and transmitting the LIN and callback number to the PSAP. The apparatus that may be used in conjunction with this method includes database management means, emergency number detection means, call routing means, ISDN and non-ISDN signaling means. The apparatus may be configured so that either the callback number, the LIN, or both are transmitted to the PSAP. Further, the apparatus may be configured to recognize multiple emergency numbers and to give emergency calls priority over non-emergency calls. The specificity of the LIN can be determined by the system administrator and additional text information may be associated with the LIN. The call routing and signaling means are capable of routing the emergency call through multiple PBX/MLTS systems before reaching the public network.
However, a situation may occur where a caller immediately disconnects an emergency call before the LIN/callback number can be transmitted to the PSAP. Such a situation might occur in different ways, e.g. criminal activity forcing unintentional hang-up, accidental dialing followed by intentional hang-up, an emergency requiring immediate flight, etc. The PSAP may receive the primary billing number but not the accurate LIN/callback number. This results in ambiguity for the PSAP. It may be impossible to determine whether the call was a mistake or whether and where the emergency is.
Another method may be used for accurately reporting the LIN of an emergency caller behind a PBX/MLTS system to a PSAP even when the caller immediately disconnects. According to this method, LIN/callback number information is buffered immediately upon the detection of an emergency call, upon the detection of an on-hook event prior to transmitting the LIN/callback number information, a timer is activated and LIN/callback number information is transmitted from the buffer before the timer expires. When the timer expires, the call is disconnected.
However, a situation may occur where the caller does not have DID capability such as in a hotel room. In the state of the art PBX/MLTS systems it is usually impossible to provide an accurate DID call back number to a PSAP when the call is made from a station which is not able to receive direct inward calls.
It is therefore an object of the invention to provide methods and apparatus for accurately reporting the DID of an emergency caller behind a PBX/MLTS system to a PSAP.
It is also an object of the invention to provide methods and apparatus for providing a DID for an emergency caller behind a PBX/MLTS system to a PSAP where the emergency caller is not normally allowed to receive direct incoming calls.
It is another object of the invention to provide methods and apparatus for providing a DID for an emergency caller behind a PBX/MLTS system to a PSAP that do not interfere with the features of the PBX/MLTS.
In accord with these objects which will be discussed in detail below, the methods according to the invention include assigning a special DID number for use by non-DID stations behind the PBX/MLTS, detecting when a non-DID station dials an emergency number, storing the station number of the non-DID station which dialed the emergency number, setting an emergency flag and a countdown timer, forwarding the special DID to the PSAP, detecting a call to the DID, routing the call to the DID to the stored station number so long as the timer has not expired, and dropping the emergency flag when the timer expires. An apparatus according to the invention includes a PBX switch coupled to a number of local stations, at least some of which are non-DID stations. The PBX preferably includes a processor, software, and a number of storage registers. The PBX software is modified to carry out the methods described above.
According to an alternate embodiment of the invention, several special DID numbers are reserved for use by groups of non-DID stations in different locations at a facility. For example, in a facility which spans a first and second floor and utilizes a single PBX switch for stations on both floors, it may be advantageous to provide one DID number for the non-DID stations on one floor and a different DID number for the non-DID stations on the other floor.